In the processing of semiconductor wafers of silicon and the like in the manufacture of integrated circuit (IC) chips, etching of oxide layers or films on the surface of the wafer is an important aspect of the processing.
Much of the wafer processing in the past has utilized a wet etching process. This involves spraying a liquid acid and other liquid chemicals onto silicon wafers followed by rinsing with de-ionized water. The wafers are typically confined in wafer carriers, formed of a material capable of withstanding the deteriorating effects of strong chemicals such as acids.
One such etching apparatus includes wafer carriers carried on a variable speed turntable or rotor in a closed bowl. Such a machine has many variable phases in its operation including varying the speed of the rotor, sequentially spraying various liquid processing chemicals, and introducing nitrogen gas for drying the wafers between various wet processing phases. One such acid processor is illustrated and described in U.S. Pat. No. 3,990,462. U.S. Pat. Nos. 4,609,573; 4,682,615; and 4,691,722 also disclose variations in spray nozzle arrangements and other facilities for wet etch processing. Additionally, U.S. Pat. No. 4,682,614 discloses a nearly horizontal, wet-etching machine.
Etching of silicon wafers has also been carried out with plasma of certain gases. U.S. Pat. No. 3,879,597 discloses apparatus for simultaneously etching a number of wafers using plasma techniques.
Etching of oxide films on silicon wafers has been accomplished, in more recent years, with the use of anhydrous hydrogen fluoride gas. See, for instance, U.S. Pat. No. 4,749,440. The etchant hydrogen fluoride gas is usually diluted with dry nitrogen gas. A small amount of moisture, either as a vapor mixed with the hydrogen fluoride gas or contained in the oxide film being etched, is necessarily present to react with the oxide in the film to initiate the etching process.
U.S. Pat. No. 4,900,395 discloses a method and apparatus for etching a batch of wafers in a rotating bowl and processing chamber with the wafers being stacked horizontally around a central spray tube. In a second embodiment, the wafer carrier is rotated within a drum having multiple nozzles. A third embodiment has a processing chamber at an almost horizontal position, again rotating a drum containing a wafer carrier holding wafers stacked almost vertically on edge.
In most of these processes, for both wet etching and gaseous etching, there is a rotating inner chamber that holds the wafers or wafer carriers so as to evenly diffuse the gas or liquids over the wafer surfaces. The use of a rotating inner chamber necessitates the use of bearings and other moving parts which are degraded by the extremely corrosive nature of the etchants. Moreover, the wafers must be rinsed after etching by a separate apparatus. This necessitates exposure of the etched wafer to atmosphere during movement of the wafers to the rinsing apparatus and introduces another variable which adversely affects the processed wafer.
It is thus a object of this invention to provide a simpler, no-moving-parts wafer etch chamber that is not affected by corrosive etchants. It is a further object of the invention to provide an apparatus that automatically sequentially processes a batch of wafers by a process which washing the wafers with a cascade water flow of deionized (DI) water, cleaning the chamber by a spray rinse, and, finally, drying the chamber in preparation for the next batch of wafers. This process is performed with no exposure of the wafers to the atmosphere.
It is another object of this invention to provide an automated control means that follows a programmed sequence to control the etching process including directing of HF gas, N.sub.2, and DI water onto the wafers and the discharge of these gases and liquids.
Since rotation involves mechanical friction and wear of parts creating undesirable particulate and additional maintenance, it is another object of this invention to eliminate the need to rotate the wafer carrier or the spray or gas nozzles. Additionally, the acid etcher is adapted for use with commercially available 150 mm wafer carriers, i.e., a wafer carrier formed in a box-shape, approximately 150 mm on a side, capable of carrying 25 wafers each.
It is another object of this invention to provide a self-contained apparatus that houses an etch chamber, valves, controls, piping, tanks, meters, and gas storage.